Lecture 25: I/O IntroductionMotivation: Who Cares About I/O?I/O SystemsTechnology TrendsStorage Technology DriversHistorical PerspectiveDisk HistorySlide 8Slide 9MBits per square inch: DRAM as % of Disk over timeAlternative Data Storage Technologies: Early 1990sThe ÆtherStore View (World-wide data)Properties of ÆtherStoreDevices: Magnetic DisksDisk Device TerminologyCS 252 AdministriviaTape vs. DiskCurrent Drawbacks to TapeAutomated Cartridge SystemRelative Cost of Storage Technology—Late 1995/Early 1996Disk I/O PerformanceResponse Time vs. ProductivityResponse Time & ProductivityDisk Time ExampleBut: What about queue time? Or: why nonlinear responseDeparture to discuss queueing theoryIntroduction to Queueing TheoryA Little Queuing Theory: NotationA Little Queuing TheorySlide 30A Little Queuing Theory: Variable Service TimeA Little Queuing Theory: Average Wait TimeA Little Queuing Theory: M/G/1 and M/M/1A Little Queuing Theory: An ExampleA Little Queuing Theory: Another ExampleA Little Queuing Theory: Yet Another ExampleProcessor Interface IssuesI/O InterfaceMemory Mapped I/OProgrammed I/O (Polling)Interrupt Driven Data TransferDirect Memory AccessInput/Output ProcessorsRelationship to Processor ArchitectureSlide 45SummarySummary: Relationship to Processor ArchitectureJDK.F98 Slide 1Lecture 25: I/O IntroductionProf. John KubiatowiczComputer Science 252Fall 1998JDK.F98 Slide 2Motivation: Who Cares About I/O?•CPU Performance: 60% per year•I/O system performance limited by mechanical delays (disk I/O)< 10% per year (IO per sec or MB per sec)•Amdahl's Law: system speed-up limited by the slowest part!10% IO & 10x CPU => 5x Performance (lose 50%)10% IO & 100x CPU => 10x Performance (lose 90%)• I/O bottleneck: Diminishing fraction of time in CPUDiminishing value of faster CPUsJDK.F98 Slide 3I/O SystemsProcessorCacheMemory - I/O BusMainMemoryI/OControllerDisk DiskI/OControllerI/OControllerGraphicsNetworkinterruptsinterruptsJDK.F98 Slide 4Technology TrendsDisk Capacity now doubles every 18 months; before1990 every 36 motnhs• Today: Processing Power Doubles Every 18 months• Today: Memory Size Doubles Every 18 months(4X/3yr)• Today: Disk Capacity Doubles Every 18 months• Disk Positioning Rate (Seek + Rotate) Doubles Every Ten Years!The I/OGAPThe I/OGAPJDK.F98 Slide 5Storage Technology Drivers•Driven by the prevailing computing paradigm–1950s: migration from batch to on-line processing–1990s: migration to ubiquitous computing»computers in phones, books, cars, video cameras, …»nationwide fiber optical network with wireless tails•Effects on storage industry:–Embedded storage»smaller, cheaper, more reliable, lower power–Data utilities»high capacity, hierarchically managed storageJDK.F98 Slide 6Historical Perspective•1956 IBM Ramac — early 1970s Winchester–Developed for mainframe computers, proprietary interfaces–Steady shrink in form factor: 27 in. to 14 in.•1970s developments–5.25 inch floppy disk formfactor (microcode into mainframe)–early emergence of industry standard disk interfaces»ST506, SASI, SMD, ESDI•Early 1980s–PCs and first generation workstations•Mid 1980s–Client/server computing –Centralized storage on file server»accelerates disk downsizing: 8 inch to 5.25 inch–Mass market disk drives become a reality»industry standards: SCSI, IPI, IDE»5.25 inch drives for standalone PCs, End of proprietary interfacesJDK.F98 Slide 7Disk HistoryData densityMbit/sq. in.Capacity ofUnit ShownMegabytes1973:1. 7 Mbit/sq. in140 MBytes1979:7. 7 Mbit/sq. in2,300 MBytessource: New York Times, 2/23/98, page C3, “Makers of disk drives crowd even mroe data into even smaller spaces”JDK.F98 Slide 8Historical Perspective•Late 1980s/Early 1990s:–Laptops, notebooks, (palmtops)–3.5 inch, 2.5 inch, (1.8 inch formfactors)–Formfactor plus capacity drives market, not so much performance»Recently Bandwidth improving at 40%/ year–Challenged by DRAM, flash RAM in PCMCIA cards»still expensive, Intel promises but doesn’t deliver»unattractive MBytes per cubic inch–Optical disk fails on performace (e.g., NEXT) but finds niche (CD ROM)JDK.F98 Slide 9Disk History1989:63 Mbit/sq. in60,000 MBytes1997:1450 Mbit/sq. in2300 MBytessource: New York Times, 2/23/98, page C3, “Makers of disk drives crowd even mroe data into even smaller spaces”1997:3090 Mbit/sq. in8100 MBytesJDK.F98 Slide 10MBits per square inch: DRAM as % of Disk over time0%10%20%30%40%50%1974 1980 1986 1992 1998source: New York Times, 2/23/98, page C3, “Makers of disk drives crowd even mroe data into even smaller spaces”470 v. 3000 Mb/si9 v. 22 Mb/si0.2 v. 1.7 Mb/siJDK.F98 Slide 11Alternative Data Storage Technologies: Early 1990sCap BPI TPI BPI*TPI Data Xfer AccessTechnology (MB) (Million) (KByte/s) TimeConventional Tape:Cartridge (.25") 150 12000 104 1.2 92 minutesIBM 3490 (.5") 800 22860 38 0.9 3000secondsHelical Scan Tape:Video (8mm) 4600 43200 1638 71 492 45 secsDAT (4mm) 1300 61000 1870 114 183 20 secsMagnetic & Optical Disk:Hard Disk (5.25") 1200 33528 1880 63 3000 18 msIBM 3390 (10.5") 3800 27940 2235 62 4250 20 msSony MO (5.25") 640 24130 18796 454 88 100 msJDK.F98 Slide 12The ÆtherStore View(World-wide data)JDK.F98 Slide 13Properties of ÆtherStore•Serverless, Homeless, Encrypted data–Easy sharing of information between anyone, anywhere–Caching of data anywhere–Dynamic construction of data distribution trees–Storage can be contributed by many different companies, just like phone service. •Separating the “Where” from the “What”–View world as “ocean of data”•Highly-available: data always duplicated–Higher-probability access.–Disaster recovery: “big-one” in California doesn’t destroy your data.•Wireless devices plug in anywhere!JDK.F98 Slide 14Devices: Magnetic DisksSectorTrackCylinderHeadPlatter•Purpose:– Long-term, nonvolatile storage– Large, inexpensive, slow level in the storage hierarchy•Characteristics:– Seek Time (~10> anq ms avg)»positional latency»rotational latency• Transfer rate–About a sector per ms (5-15 MB/s)–Blocks• Capacity–Gigabytes–Quadruples every 3 years (aerodynamics)7200 RPM = 120 RPS => 8 ms per rev ave rot. latency = 4 ms128 sectors per track => 0.0625 ms per sector1 KB per sector => 16 MB / sResponse time = Queue + Controller + Seek + Rot + XferService timeJDK.F98 Slide 15Disk Device TerminologyDisk Latency = Queuing Time +
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